Design and construction of a new Mechanised Cement Bound Macadam (MCBM)

Abstract

The paper describes the development and implementation of a new heavy-duty pavement design and construction technique. The pavement structure consist of a very densely packed and interlocked, mainly single sized large aggregate skeleton, combined with a low cement and fines void filler. The small percentage of cemented finer particles specific to the gradation ensures optimal void fill is achieved without causing separation of the inter-locked large stone particles. This enables direct load transfer to take place between the interlocked large stone particles. The heavy-duty pavement is modelled on the original macadam pavement philosophy with specific reference to cement-bound macadam. However, the advances in modern day construction equipment, and an increased focus on productivity, resulted in the demise of this traditional labour-intensive method. The greatest challenge, therefore, was to mechanise the cement-bound macadam concept, while also ensuring consistent aggregate gradation production and placement. This was achieved through the innovative use of modern recycling equipment and aggregate blending plants. Performance testing of in-situ core and beam cut test samples shows the strength characteristics achieved are similar to lean mix and conventional concrete. The cost of a mechanised cement bound macadam (MCBM) layer is approximately a third to a quarter of an equivalent thickness structural asphalt layer in New Zealand. It is therefore a viable design alternative to structural asphalt, delivering performance more akin to rigid lean-mix pavements, at significantly reduced cost.